To guarantee optimum charging of a shaft furnace, it is desirable for the materials stored in the storage hopper to be distributed fairly uniformly. However, it is difficult to distribute the charge materials uniformly in the hopper because of the particle size of the charge material. The problem is that the charge material, whether it be iron ore particles or coke particles, has a varying and non-uniform particle size. As the material is conveyed towards the hopper, for example via a conveyor belt, the fine particles have a tendency to build up in larger proportions at the bottom of the layer of conveyed material, while the large particles remain in the upper part of the layer.
It then follows that when the material is tipped out of the conveyor belt, the material drops in the form of a curtain of a certain width, of which the rear layer, viewed in the direction of conveying, contains a predominance of large particles while the front layer contains more fine particles. This distribution of the particles in the curtain of material has the effect that, after loading, the rear part of the hopper, viewed in the direction in which the material is conveyed, contains more large particles than the front part and that the distribution of material is therefore distinctly non-uniform.
In addition, when the charge material impacts the hopper, a natural pouring cone is formed around the fall line. The largest and heaviest particles therefore have a tendency to tumble along the slopes of this cone, under the influence of their weight, toward the peripheral regions of the chamber. By contrast, the smallest particles, known as “fines” have a tendency to remain in the central region of the pouring cone. This phenomenon further accentuates the segregation of the material within the hopper.
To solve this problem, it has been proposed that the hopper be made to revolve about a vertical axis during loading. By virtue of the rotation of the hopper, the effects of the segregation in the curtain of material on the distribution of the material in the hopper can be reduced. Unfortunately, the segregation of the material due to the pouring cone within the hopper cannot be reduced. Such a rotary hopper cannot therefore meet the requirements of uniform charging of a shaft furnace. In addition, such a rotary hopper needs to be housed in the framework of the shaft furnace on rolling bearings. Given the size and weight of such a hopper, this step entails a considerable investment and poses problems in terms of installation maintenance.